Help composing Personal autocorrelation function

Question

Ishmael 2012-4-2

1
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/34226-help-composing-personal-autocorrelation-function

The following is my code for calculating the autocorrelation:

 function [Rxx]= myauto(x)
% This function Estimates the autocorrelation of the sequence of 
% random variables given in x as: Rxx(1), Rxx(2),…,Rxx(N),
% where N is Number of samples in x.
N=length(x);
Rxx=zeros(1,N);
for m=1: N+1
    for n=1: N-m+1
        Rxx(m)=Rxx(m)+x(n)*x(n+m-1);
    end;
end;
plot(Rxx)

The challenge, however, is that after I plot the values I get from my autocorrelation function (i.e Rxx), only half the points that I would otherwise get with the Matlab function xcorr are produced. For example, If I were to plot the autocorrelation of sin(x) [for x from 0 to 2pi], my function would only produce half of the curve that the Matlab function would.

I, thus, need help adjusting my function so that I am able to replicate the results that I get using the Matlab xcorr function.

Thanks.